Field of the Invention
The present invention relates to a laser processing apparatus which irradiates a laser beam for forming a modification layer serving as a start point of division on a wafer.
Description of the Related Art
In order to divide a wafer, on which devices such as an IC (Integrated Circuit) and so forth are formed, into a plurality of chips, a processing method for a wafer wherein a laser beam is focused on the inside of the wafer to form a modification layer serving as a start point of division has been proposed (refer to, for example, Japanese Patent Laid-Open No. 2005-86161). With this processing method, it is possible to reduce the cutting margin (cutting width) and suppress chipping (chipping of the chip) in comparison with conventional processing methods which uses a cutting blade. Further, with this processing method, also it is possible to process a wafer without using water.
Incidentally, in a laser processing apparatus used for the processing method described above, it is possible to easily switch between irradiation and non-irradiation of a laser beam. Therefore, a method has been proposed which takes advantage of this characteristic of the laser working apparatus to process a wafer of the so-called multi-project type in which devices of different shapes and different sizes are provided in a mixed state (refer to, for example, Japanese Patent Laid-Open No. 2010-123723).